Refers to hygienic supplies kept in your car in order to get cleaned up after a night out. Items such as; mouth wash, tooth brush, moist towelettes, water bottles, extra clothes, crackers (after a drunken night), etc.

Amber woke up at a friends house, desperately needing to get cleaned up before she went to church with her parents. Good thing she's able to take a car shower to wash off last night's shame.